The average American family spends about 18% of their total energy bill on hot water. That’s about $400 per year to heat water with natural gas—or about $650 with an electric water heater. In warmer states, such as California, about half the gas bill is for heating water. The average American household could save as much as 50% on both its water bill and the cost of energy used to heat that water by making its water system more efficient. Fewer than 1% of American households use solar water heating, which might handle up to 75% of the remaining water-heating load.